Environmental alarm systems such as fire, smoke, and passive infrared systems, for example, generally comprise a central controller ("control panel") connected by wires or radio frequency transmission to multiple sensing stations ("sensors") placed in strategic remote locations. In some "passive" systems the control panel simply gives an indication that something is wrong. In other "addressable" systems more specific information can be obtained by periodically polling the remote sensors.
Environmental sensors such as fire, smoke, and infrared detectors usually produce analog voltage or current output signals. The amount or density of detected smoke, the temperature sensed by a heat sensor, or sensor performance degradation can be conveyed by variations in the voltage or current of the output signal. When a system is addressable, the address of each sensor is a coded analog signal. This allows a message from a sensor to include information about a monitored environmental condition along with the location of a source of smoke, an unauthorized entry into a space, or other detected alarm-producing conditions, for example. The identification signal is usually a pattern of current pulses compliant with a protocol established by the design of the alarm system. An example of a communication protocol for environmental alarm systems is described in co-pending application Ser. No. 08/204,473, filed Mar. 1, 1994, and assigned to the assignee of the present application.
Remote sensors require periodic maintenance to maintain reliability. When servicing remote sensors, field maintenance personnel must be able to verify sensor functionality, sensitivity, and diagnostic signals. Certain prior physical security alarm system sensors have incorporated a simple visual signal, such as a single light-emitting diode, to indicate information such as whether the sensor is operating, whether there is an alarm condition, or whether a battery power supply has sufficient voltage for continued operation of the sensor.
In the past, sensor address identification signals could be verified, however, only by conducting a test of the system through the control panel. Such tests also required correlation of identification signals with sensor location. Prior techniques have used a portable digital voltmeter, temporarily connected to a sensor to obtain a digital display of analog signal output information such as condition information and address identification signals. However, such testing is inconvenient and may be hazardous depending upon the location of the sensor.
What is needed, therefore, is an improved environmental alarm system having centralized control of local information display. For example, information such as sensing element sensitivity, currently programmed address coding, an indication that an alarm condition is being sensed, the existence of a fault or degradation of performance in the sensing device, the need for sensor cleaning, an indication of the actual value being sensed, and indications of whether the sensing device is being interrogated by the central control panel should be visible on the sensor assembly itself.